DESIGN STUDY OF INDUCTION DESIGN STUDY OF INDUCTION COIL FOR GENERATING COIL FOR GENERATING

MAGNETIC FIELD FOR CANCER MAGNETIC FIELD FOR CANCER HYPERTHERMIA RESEARCHHYPERTHERMIA RESEARCH

V. Nemkov, R. Ruffini, R. Goldstein, J. Jackowski – AMF Life

Systems, LLC, Michigan, USA

T. L. DeWeese, R. Ivkov - Department of Radiation Oncology and

Molecular Radiation Sciences, Johns Hopkins University School of

Medicine

OverviewOverview• Coil Design for Low Volume In Vitro and

Small Animals Research

• Coil Design for Large Volume In Vitro Research

• Magnetic Field Distributions for 2D and 3D models

• Parameter Comparison for Different Coils

• Temperature Distribution in Magnetic Core

• Conclusions

Induction Coil for Low Volume In Induction Coil for Low Volume In Vitro and Small Animals ResearchVitro and Small Animals Research

Coil features: - Planar turns with gap variation - Fluxtrol magnetic “caps” on the coil ends

Magnetic field distribution along the center line

-5

-4

-3

-2

-1

0

1

2

3

4

5

0 200 400 600

Field Strength (Oe)

Dis

tanc

e A

long

Cen

ter

Line

(cm

)

Magnetic Field MappingMagnetic Field Mapping

Induction coil with Field Probe on the stand

Power supply 3 kW

Large Volume Cell Culture CoilLarge Volume Cell Culture Coil• Goal: Design an inductor with even flux density

for heating of culture specimens• The region of concern is a specimen holding

dish (24 or 96-well dish)• Frequency must be 140-160 kHz

• Max flux density Bm=400 Gs

• Thermal influence of the

coil on the cell dish

must be minimal

Concept of New Induction CoilConcept of New Induction Coil

Cooling plate

Coil tubes

Magnetic controller

Coil “opening” dimensions: A x B x H = 110 x 175 x 40 mm

A

Inductor withInductor with Magnetic CoreMagnetic CoreChallenges:

- 3D System - Intensive heating of magnetic core due to

strong field, high frequency and long cycle time

Core temperature control: 1. Material selection with account for orientation 2. Intensive heat transfer to copper through a layer

of thermo-conductive epoxy compound3. Use of additional cooling plate4. Coil copper design with reduced 3D effects

Flux Flux DensityDensity Map of Rectangular Coil Map of Rectangular Coil with Magnetic Corewith Magnetic Core

Flux 2D program

Temperature Maps in 2D ApproachTemperature Maps in 2D Approach

a – Core of Fluxtrol 50; b – Core of oriented Fluxtrol 75

Flux density 400 Gs

Tmax = 140 CTmax = 240 C

Induction Coil with Extended Induction Coil with Extended Cross LegsCross Legs

Cooling plate

Extended Cross Legs

Slot for thermal protection screen

Temperature Prediction for the Temperature Prediction for the Core Made of Oriented Fluxtrol 75Core Made of Oriented Fluxtrol 75

a b

Uniform coil winding Winding with widened cross-over leg

Coil Type Core Program Bm (Gs)

U (V)

I (kA)

S (MVA)

P (kW)

Helmholtz None Flux 2D 400 1750 8.4 14.7 74

Rectangular Fluxtrol 50

Flux 2D 400 650 3.8 2.5 24

Rectangular Fluxtrol 50

Flux 3D 400 720 3.3 2.4 26

Widened Cross-Leg

Fluxtrol 75

Flux 3D 400 660 3.5 2.3 25

Electrical Parameters for Helmholtz Electrical Parameters for Helmholtz Coil and Rectangular CoilsCoil and Rectangular Coils

Laboratory TestsLaboratory Tests

Power supply 25 kW

Frequency 150 kHz

Used power 18 kW

Coil head voltage 480 V

Magnetic field density 280 Gs

Maximum core temperature 1000C

Magnetic Flux Density DistributionMagnetic Flux Density Distribution

Plot of magnetic flux density through the center of the inductor

15

Induction Equipment at JHUInduction Equipment at JHU

Inductor and capacitor battery Power Supply 80 kW

SummarySummary• Induction coils for small volume tests require careful

manufacturing to provide uniform magnetic field in test area; power supply may be small – 3 -12.5 kW for field density 500 - 1000 Gs

• Design of induction system for large cell-well plates is a challenging task

• Helmholtz coils require much higher reactive power (6x), active power (3x), voltage and current than a special coil with magnetic concentrator

• 2D simulation resulted in overvaluation of coil current (24%) & undervaluation of voltage (10%) vs. 3D

SummarySummary

• 3D effects lead to significant increase of the magnetic core temperature especially in the corners

• Extension of cross leg copper significantly reduces 3D effects and diminishes local flux density and core temperature

• Special attention must be paid to magnetic material selection, orientation and application technique

• Fluxtrol 75 with optimal orientation and thermally conductive glue provides the best results

• Results of the coil tests were in good agreement with predicted values

AcknowledgementAcknowledgement

This work was funded by a grant from

the Prostate Cancer Foundation